Depends on your version of PowerPoint. Right click your image and see if you
get a pop up menu with a "Save as Picture" option. If so save your image in
a format of your choice.
Which version of PowerPoint are you using? AFAIK, there are no free updates.
You however, depending on your version be able to purchase an update version
for a cheaper price than a full new version you might also want to look here http://office.microsoft.com/en-ca/downloads/default.aspx?ofcresset=1
But first, try saving your presentation as Web Page. The specifics are a bit
different for each version, but try File, Save As Web Page; don't choose the
Single File option.
When you do the save, it'll create an HTML file wherever you asked it to and also
a folder full of support files. Among them will be all of the original images
that went into your PPT file.